A place suitable for oil-gas accumulation and forming an oil-gas reservoir is called as a trap (or oil-gas trap). Currently, the trap concept is an important theory of searching for oil and gas. No oil or gas can exist if there is no trap. But for a long time, the structural trap is still mainly evaluated with the structural uplift amplitude and the structural area. However, it is difficult to quantitatively measure the actual trap amount just according to the above two indexes. As to the fault block trap, generally the trap area is only estimated according to the fault block area, while detailed studies on the key issue, i.e., whether the fault block has the trap condition are absent.
At present, commercial softwares for estimating the fault sealing ability, the structural spill point and the trap amount still stays in qualitative analysis or underground reservoir analysis based on two-dimensional data. The conventional method is to make an overlay diagram of sand-body structures on both sides of the fault on the two-dimensional profile, so as to determine the fault plane spill point of each sand layer, and find each sealing boundary point; and project those sealing boundary points to the structural contour plane and connect them with lines, so as to calculate the sealing area and the trap amount. However, when the above conventional method is used to evaluate the sealing ability of a complex fault block formed by many faults, it is very difficult to accurately analyze the sand layer communication in a two-dimensional space and the overall sealing condition just using the lithological two-dimensional butting profiles on both sides of a series of faults, thus an accurate result is hard to be obtained.